Q & A: Can you bend light with light?

Most recent answer: 12/10/2013
Q:
Just a novice that loves listening to and attempting to fathom some. Given the Theory of General Relativity, and that gravity can bend light by virtue of its abilty deform spacetime. Has the amount of gravity needed to bend light been be quantified? If it has (I would assume) then realtionship of energy to mass, with mass "generating" gravity.. there should be value for energy wherein energy in and of itself could bend light. True? Given there has been calculated a value for how much gravity is needed to bend light then we would have a value of how much energy is needed to also bend light. Could you relate that value to some earthbound value? Also was has been repeated eletric and magnetic forces/energy are NOT the gravity. So what kind of energy would be used to bend light given there was enough. Wow.. and come to think of it.. if gravity is affecting spacetime and thus able to bend light... then too energy ( given enough) would be able to bend spacetime as well. Yes? Thanks for reading!
- Frank (age 50)
Clinton MS USA
A:

Hello Frank,

Yes, in principle but not in any practical sense.  The fact that mass can bend light is a well calculated and well measured phenomenon.  The first example occurred  soon after Einstein developed the general theory of relativity.   The measured deviation of distant light from stars was measured during a total eclipse of the sun.  The bending angle is proportional to mass of the object causing it.  The mass of the sun is enormous but the measured angular deviation was only about 1.5 arc seconds, 0.0004 degree.

The effective mass of any light source that I can think of would not even come close to a microgram of equivalent mass energy.   No way can you measure the corresponding deflection it would cause a light beam. Still it's an interesting question, just don't hold your breath.

LeeH

(published on 12/10/2013)